1. Field of the Invention
This invention relates to a method of making a magnetic head for perpendicular magnetization recording and reproducing, which conducts high-density recording and reproducing.
2. Description of the Prior Art
As a system for recording information in a magnetic recording medium, for example, a magnetic tape or magnetic disk, and reproducing the information therefrom, there has heretofore been widely used a system wherein the magnetic layer of the magnetic recording medium is magnetized horizontally with respect to the surface of the magnetic layer.
The magnetic head used in the aforesaid recording and reproducing system is generally called a ring type head. The ring type head exhibits a high reproducing efficiency. However, since there is a large reduction in the magnetic field intensity generated in the recording bit, it is not always possible for the ring type head to achieve high-density recording.
Recently, it has been proposed to employ a perpendicular magnetization recording and reproducing system capable of conducting high-density recording, instead of the intra-surface recording and reproducing system using the aforesaid ring type head, i.e. the horizontal magnetization recording and reproducing system. In the perpendicular magnetizationrecording and reproducing system, the magnetic layer of the magnetic recording medium is magnetized perpendicularly to the surface of the magnetic layer. This system is being proved to be basically very excellent.
In the aforesaid perpendicular magnetization recording and reproducing system, in order to satisfactorily conduct perpendicular magnetization recording, it is first necessary to use a magnetic recording medium exhibiting magnetic anisotropy perpendicular to the recording surface. Further, it is essential to use a magnetic head capable of generating the magnetic field component perpendicular to the recording surface in a sharp distribution pattern.
As the magnetic recording medium for the perpendicular magnetization recording, it is known that a sputtered Co-Cr film or a deposited Co-Cr film is suitable.
FIG. 1 is a sectional view showing the relationship between a recording medium and an ordinary auxiliary magnetic pole excitation type head for perpendicular magnetization recording. As the magnetic head for the perpendicular magnetization recording described above, the auxiliary magnetic pole excitation type head as shown in FIG. 1 is widely used. This magnetic head comprises a flat plate-like main magnetic pole 2 positioned on the magnetic layer side of a magnetic recording medium 1, and an auxiliary magnetic pole 3 provided with an exciting coil 4 therearound and positioned on the side opposite to the magnetic layer.
The magnetic head as described above is excellent in that it generates a magnetic field exhibiting a sharp distribution pattern in the direction perpendicular to the recording surface. However, when the recording bit is narrower than the thickness (t) of the main magnetic pole 2, the magnetic pole 2 extends over the recording bits magnetized in the directions reverse to each other as indicated by the arrows. Therefore, in the reproducing step, the magnetic flux is circulated without crossing the coil 4. As a result, the reproducing output is markedly decreased. When the thickness (t) (in general, within the range of 3 .mu.m to 1 .mu.m) of the main magnetic pole 2 is double the bit length, the reproducing output disappears.
FIG. 2 is a graph showing the recording density characteristics of the magnetic head of FIG. 1, i.e. the relationship between the reproducing output and the bit density in the system of FIG. 1. In the output change pattern shown in FIG. 2, the point a indicates the case wherein the bit length is half the thickness (t) of the main magnetic pole 2, and the point b indicates the case wherein the bit length is a quarter of the thickness (t) of the main magnetic pole 2.
In order to eliminate the drawback of the conventional perpendicular magnetization recording and reproducing head, it has been proposed in Japanese Unexamined Patent Publication No. 57(1982)-40723 to use a magnetic head wherein the thickness of the main magnetic pole is continuously changed in the width direction of the track, thereby to prevent the reproducing output from decreasing sharply.
However, the magnetic head disclosed in aforesaid Japanese Unexamined Patent Publication No. 57(1982)-40723 is made by a method wherein a thin film having a uniform thickness and made of a soft-magnetic metal such as permalloy, Sendust or an amorphous magnetic material formed on a substrate by sputtering or the like is abraded so as to continuously change the film thickness in one direction. Therefore, it is not always possible to accurately obtain desired film thicknesses for reasons of processing accuracy, and the electromagnetic transducing characteristics of the magnetic head are not always satisfactory.